RESUMO
The effect of single and repetitive electrical stimulation of the dorsal columns on cells in laminae IV and V of the ipsilateral dorsal horn at S1 was examined in spinalized cats. About two-thirds of the cells responded to thermal nociceptive cutaneous stimulation and of these most responded also to low threshold mechanical stimulation. The other one-third of the cells were innervated by mechanoreceptors including type I or Haarscheiben. A single shock to the dorsal columns typically caused short latency activation of the cells, followed by inhibition lasting about 100 msec. Several minutes of repetitive dorsal column stimulation (DCS) at 3 Hz or 50 Hz had no prolonged effect on about two-thirds of the cells. The rest of the cells were less responsive for up to 30 min after the cessation of 50 Hz. Assuming that the studied interneurons have a pain-mediating function, the results indicate that some cumulative and poststimulatory DCS suppression of pain may be ascribed to spinal mechanisms. The more effective and longer lasting suppression produced by DCS in pain patients would, however, be dependent on other types of interneurons, on suprasegmental loops and/or on effects on pathophysiological mechanisms which may be operative in the chronic pain state. The lack of cumulative inhibition in most of the cells in this study is compatible with the previous observation of a retained perception of acute pain during DCS in man.
